Obviously to start with you need the right materials to build a base like this.  For mine, I started with cork pot-mats you use to put your steaming hot pots onto the bench top so you don’t burn the surface.  These are excellent because I found them readily available at my local supermarket and they are thick and have a fine cork grain.  I haven’t found many cork tiles that are this thick, so these are my favourite cork supply at the moment.

It’s easy to make the texture using this cork, all you have to do is break off chunks and glue them down.  Then once the glue is dry have at it with a sharp tool and gouge and rough it up until you get a nice rough, rocky surface.  I like to then use cheap superglue to strengthen any areas that might be weak.  If you want to you can simply smother superglue over the entire base if you like.  This makes it more likely to resist chipping and breaking.  Make sure you make the bases before you put the model on it.  Nothing worse than superglue in the details of a model, let me tell you now!

So!  You’ve done the base.  It looks how you want it to, you’ve left the smooth areas for the lava floe and it looks about ready to go.  BUT!  The flat areas don’t look like lava yet.  Here’s how I make the lava look sweet.

First of all, you want to create some bubbles in the lava.  We all know that lava has to be bubbling, it’s just a law of… stuff.  It just doesn’t look cool unless you have some bubbles in it, trust me!  So what I have been using is a combination of materials.  To make big bubbles, I have found large round headed pins to be a great resource.  Just get a pair of cutters and chop the ball in half, select the best looking bit and glue it down.  For small bubbles I have been using Sago palm starch balls, glued down in the same fashion.  Usually I just arrange them how I want and then surreptitiously drop a glob of superglue on top.  That sets them in place.

Secondly, smear the area with a thick helping of PVA or white glue.  Don’t let it get onto the rocky areas except at the edges where the lava would touch.  Let it go up the edges a bit so that it looks a little like the stone is melting.  Make sure you also liberally cover the lava bubbles to smooth them into the whole picture.  You may need to apply a few layers of the PVA to make this look effective, but keep going.  Wait till it dries between layers so you know how much you need to do.

Now you should have your bases looking right to go.  Once they are dry, undercoat them however you like.  I normally would use a flat black spray of some kind.  One thing I should mention is, after the base is dry I personally attach the model too.  That’s my preference mainly because of the way I work.  You may be able to visualize the overall effect without having the two together, but I need them together to get the whole effect coherent.

I haven't provided any photos of this up till now, because it's all pretty straightforward.  You can see from the first few pics of the models what the lava will start to look like once you have created the rocky ground and lava floe with it's bubbles.  I didn't attempt to make crusty lava, my intention with the Iron Giants is to create a flowing liquid lava effect.  Realistic?  Who cares!

Here’s where we get to the painting!